1. Field of the Invention
This invention relates to a DC electric arc furnace for the heating and melting of materials.
2. Description of the Prior Art
In certain metallurgical applications it is advantageous to use a DC electric arc furnace in which the electric arc is transferred either to an electrode, typically the anode, located close to the material to be heated or melted or to the material itself. One application is where metallic oxides are used in these furnaces. In practice, carbon is added for their reduction and valuable metals are produced as a result of the electric arc reducing the melt, i.e., the material in the furnace to be melted. A stationary attachment of the arc to the reacting melt layer would produce strong temperature non-uniformities in the melt, and consequently, locally varying rates of reaction and possibly local failure of the refractory wall of the furnace. Non-uniformity of the product or product quality and possible disruption of the process may also be a consequence.
Various attempts have been made to prevent the stationary attachment of the arc to the material being heated. In U.S. Pat. No. 4,154,972, movement of the arc about the surface of the material to be melted was attempted by the precession of the arcing electrode. This furnace has the disadvantage that the arc motion is controlled at the arcing electrode whereas control of the motion of the arc at the arc attachment surface or the melt itself is desired. With this scheme, if the arc or the arc attachment at the melt is exposed to any disturbance the control of the arc motion is diminished. In U.S. Pat. No. 4,110,546, a rotating magnetic field generated by a variable frequency AC source is used to angularly deflect and rotate the arc within the furnace enclosure. There the melt forms the anode and the arcing electrode is the cathode in the DC circuit. By increasing the frequency of the AC supply to the coils, the speed of rotation of the arc is increased. A disadvantage with this arrangement is that both an expensive variable frequency AC power supply and a DC power supply must be provided to the furnace.